Ignition and safety control system for fuel burners



c. K. STROBEL 2,478,511

IGNITION AND SAFETY CONTROL SYSTEM FOR BURNERS Filed March 21, 1946 64 4 TIME DELAY RELAY H INVENTOR.

Charles K. Strobel BY W/ ATTORNEY.

Patented Aug. 9, 1 949 IGNITION AND SAFETY CONTROL SYSTEM FOR FUEL BURNERS Charles K. Strobel, Pittsburgh, Pa., assignor to Robertshaw-Fulton Controls Company, a corporation of Delaware Application March 21, 1946, Serial No. 656,029

9 Claims. 1

This invention relates to ignition and safety control systems for fuel burners and, more par; ticularly, to electrically operated systems therefor.

Systems of the type indicated may be arranged so that an electromagnetic safety valve may be opened when a main switch is closed and the fuel supply turned on. The fuel is then ignited by an electric igniter controlled by the main switch and after the expiration of a starting period the igniter is disconne ted by operation of a timing device. The valve then either remains open or is closed by varying the current supply thereto according to variations in the resistance of a thermal resistor exposed to the heat of the burning fuel.

Where an electromagnetic relay is employed in conjunction with the timing device it is apparent that power consumption and operating noise would be reduced if the power consuming element of the relay were disconnected after the starting period. Such a relay may include mercury switches having timing elements, which close a control circuit when the relay is deenergized and open the circuit after a predetermined time delay following energizati-on of the relay. The invention is directed toward the use of these standard normally closed, delayed opening switches and thus, as will appear hereinafter,

eliminates the necessity of specially designed switches which may not be commercially available.

An object of this invention is to render an ignition and safety control system for fuel burners substantially noiseless during the running period of the burner.

Another object of the invention is to effect a saving in power consumption in the operation of safety and ignition systems.

Another object of the invention is to ensure re 2 which is a schematic view of an ignition and safety control system for a gaseous fuel burner embodying thejinvention. I

Referring more particularly to the drawing, a gaseous fuel burner I0 is shown as being supplied with fuel by a main fuel pipe l2. The fuel supply is under control of a combined main fuel cock and switching means ll which may form part of a thermostatic fuel control device of well known form. The cock and switching means I is arranged for manual operation by a handle I5 carrying the usual indicia indicating the 011" and off positions. It will be apparent, however, that the main fuel cock and switching means ll could be arranged for separate operation if desired and that the thermostatic device could be dispensed with. For the purposes of clarity in illustration, the handle i5 is shown enlarged and separated from the means M in the drawing and the separated view discloses a pair of spaced cam elements l6, l1 shown as carried by the handle IS.

The cam element It is adapted to operate switching means It! by engagement with a resilient switch arm 20 thereof. The switch arm 20 carries a contact 22 which is adapted for operative engagement with a relatively fixed contact 24 when th handle I5. is rotated from off toward on position. It will be apparent that the engagement between the contacts 22 and 24 is momentary only and that the cam element It will slip past the resilient switch arm 20 prior to the handle l5 reaching the on position. Moreover, when the handle I5 is rotated in the reverse direction the contacts 22, '24 cannot become engaged.

The cam element H is adapted to operate a second switching means 26 during rotation of the handle I5 between off and on positions. The switching means 26 may take the form of a toggle arrangement having a switch lever 28 pivoted intermediate itsends andengaged by a coil spring 30 for causing the switch lever 28 to remain in the position in which it has been moved. Thus, upon rotation of the handle 15 in a counter-clockwise direction from o to on position the cam element I! will engage the switch lever 28 and cause rotation thereof on its pivot in a clockwise directlon. When this movement is completed under bias of the spring 32 the switch lever 28 makes engagement with a relatively fixed contact 32. When the handle I5 is rotated in thereverse direction, the switch arm 28 is moved outof engagement with the contact 32 and under bias of the spring 30 will remain in contact disengaged position until the handle I 'is again rotated in counter-clockwise direction.

Interposed in the fuel supply pipe I2 between the main fuel cock I4 and'the burner I8 is an electromagnetic fuel valve 34 of any known type which may be arranged, as in this instance, to be opened when current of sufficient energizing value is supplied to the solenoid 35 thereof and closed by gravity, spring or other means upon a reduction of the current value thereto below holding value. A pilot burner 36 is provided for igniting the main burner I0 and is supplied with fuel from a conduit 38 connected to the main fuel cock I4 to receive fuel from the pipe I2 when the main cock is open. It will be observed, therefore, that the electromagnetic valve 34 controls the flow of fuel to the main burner In only and the pilot burner 36 is under control only of the main fuel cock. Where the pilot burner 36 is not desired it can be dispensed with without affecting the operation of the system in its essential aspects as will be hereinafter apparent.

Thefuel issuing from the pilot burner 36 is adapted to be ignited by an electric resistance igniter 48 which has an adjusting resistance M in circuit therewith. The heat of the flame of the burning fuel is adapted to cause variation in the resistance of a thermal resistance element 42. The thermal resistance element 42 is preferably in the form of a coil of wire of material having normally a relatively low resistance and a positive temperature coefiicient of resistance and is adapted to increase-appreciably in resistance whenheated by the flame. While this resistance element 42 is also heated by passage of current therethrough and other types of ballast resistors or flame sensitive elements could be substituted, it will be understood to be primarily responsive to the heat of the flame. The igniter 40 and thermal resistance element 42 are both located in proximity to the pilot burner 36 but where this burner is dispensed with these elements will be positioned in proximity to the main burner I0. 7

A second thermal resistance element 44 is included in the system and is also formed from a coil of wire having normally a relatively low resistance and a positive temperature coefficient of resistance. This second resistance element 44 is not, however, exposed to the flame of any burner and is adapted to vary in resistance only due to the passage of current therethrough. As will be apparent to those skilled in the art, the thermal resistance characteristics of the element 44 could be dispensed with and a fixed or constant resistor employed. a

A cut-out 46 is provided for opening a circuit to the solenoid 35 of valve 34 in the event of an open circuit occurring in the thermal resistance element 42. The cut-out 46 is preferably of the thermal type having time-Jag operation. Such devices are constructed with predetermined time .current characteristics and usually contain a heater element in addition to and affecting a adapted to operate a pair of time delay switches 54, 56 which may be similar in that both open after a specified time delay and have instantaneous reset characteristics. The switch. 56 differs from switch 54 in having a longer time delay period following rotation of the handle I5 to "on position. i

The switches 54, 56 are preferably of the mercury tube type well known to those skilled in the art, and are so indicated in the drawing. The switch 56 may have a timedelay of eighteen seconds before opening following movement of the handle I5 to on position and, as stated, is adapted for instantaneous closing when the handle ismoved to off position or when thesolenoid 50 is otherwise deenergized. The switch 54 may have a time delay of five seconds before opening following movement of the handle I5 to on position and also has an instantaneous closing. The switch 54 is provided with a pair of electrodes 58, 60 and switch 56 is provided with a similar pair of electrodes 62, 64.

As indicated in broken lines in the drawing, the movement of the core 52 between attracted and released positions is adapted to operate separate pairs of switching means 66, 68. The switching means 66 comprises a relatively fixed contact I0 and a movable contact 12, the latter being operatively associated with the core 52 for engagement with the fixed contact I0 .when the solenoid 56 is energized to attract the core 52. Similarly, the switching means 68 comprises a relatively fixed contact 14 and a movable contact I6, the latter being operatively associated with the core 52 for movement into engagement with the contact I4 when the solenoid 50 is energized to attract the core 52.

fusible member which opens the circuit by the passage of overcurrent.

A control means or relay by the reference numeral 48 is provided for establishing desired circuit conditions during starting and running periods of the burner. The control relay 48 is preferably of the electromagnetic type having a solenoid winding 50 and a movable core 52 cooperable therewith. The movement of the core 52 to attracted position is designated generally Means are provided to complete the circuit manually in order that the pilot burner 36 may be lighted with a match should the ignition coil 48 fall and cause an open circuit. This means takes the form of a manually operated switch I8 which is normally held open by a'spring 80. A suitable electrical resistance element 82 in circuit with the switch 18 is included to compensate for the loss of resistance of the ignition coil 40 should this coil become open circuited for any cause.

The operation of the system will be described in connection with the circuit arrangements and is as follows: The main fuel cock and switch I4 is shown in the drawings in the off position and no fuel is being supplied to the main burner I0 or the pilot burner 36. When the handle I5 is rotated counter-clockwise toward the on" position the cam element I1 engages the switch lever 28 to operate the toggle switch 26 and cause engagement of the switch lever 28 with the contact 32. A circuit to the primary of a transformer 84 is then established by wire 86 connected at one end to contact 32 and at the opposite end to line wire 88,, by wire 90 connected at one end to switch lever 28 and at its opposite end to one terminal of the-primary of the transformer 84, and by line wire 92 connected to the opposite terminal of the primary of transformer 84.

The rotation of the dial l5 also causes the cam element I6 to operate the switching means I8 causing momentary closure of the contacts 22, 24. This contact engagement establishes a circuit to the solenoid 50 of the control relay 48 which may be traced as follows: from one terminal of the secondary of transformer 84, wire 94,'wire 96, solenoid winding 56, wire 98, wire I 00, wire I02, contacts 24, 22, wire I64 and wire I06 to the 5 opposite terminal of the secondary of transformer 84. F

The solenoid winding 50 being energized through the described circuit, the core 52 is moved to attracted position causing the time delay switches 54, 56 to'be moved into position for opening operations after the specified time delay periods. The movement of the core 52 also causes operation of the switching means 66, 68 and consequent engagement between contacts 10, 12 and 74, I6.

The circuit initially established by the described operation of the relay 48 is of the electrical bridge type. The first arm of the bridge may be traced from one terminal of the transformer secondary, wire 94, wire I08, adjusting resistor 4I, wire, H0, wire H2, igniter 40, wire I00, wire II4, contacts I6, I4 of switching means 68, electrodes 64, 62 of time delay switch 56, wire H5 and wire I I6. The second arm of the bridge from wire II'6 comprises wire H8, solenoid valve coil 35 and wire I20 which is connected to the opposite terminal of the transformer secondary by wire I06. The third arm of the bridge from the junction of wires I20 and I06 comprises wire I2I, thermal resistance element 42 and wire I22. The fourth arm of the bridge from wire I22 comprises wire I24, resistance element 44 and wire I26 which makes junction with the first arm and wire 94 to the transformer secondary. It will be observed that the source of electrical energy from line wires 88, 92 by way of the transformer 84 is connected across opposite junctions of the bridge by wires 94 and I06 which connect with the first and fourth arms and the second and third arms respectively. Thus, the first and second arm and the third and fourth arm are in series circuit, respectively, and in multiple across the junctions. The detector arm of the bridge circuit comprises the cut-out 46 having one terminal thereof connected by a wire I28 to the'junction of wires I24 and I22 and the opposite terminal thereof connected by a Wire I30 to the junction of wires H8 and H6.

The time delay switch 54 which has the shorter delay period serves to shunt the electromagnetic fuel valve 34 for this five-second period and is connected by wire I32 from wire H6, electrode 58, electrode 60, wire I34, contacts 12, I of switching means 66 and wire I36 to wire I2I. Moreover, in this starting circuit it Will be observed that the contacts 22, 24 ofthe switching means I8 do not remain in engagement whenthe dial I reaches the on position. Consequently, the solenoid winding 50 ofthe control relay 48 which was previously energized through the circuit established by switching means I8 is thereafter connected in parallel circuit with the igniter 40 and adjusting resistor 4|. The source of energy for the solenoid winding 50 through the wires I02 and I04 is eliminated for the duration of the burner starting and for the running period.

As during this starting period the elements comprising the bridge circuit are unheated and the electromagnetic valve 34 is shunted by the time delay switch 54, the bridge network is considerably unbalanced. Within a few seconds, however, the circuit elements heat up and the bridge balance is improved at the time that the time delay switch 54 opens to remove the shunt of the electromagnetic valve 34. The removal of this shunt serves to further improve the balance of the bridge. At this time the ignition coil 40 has reached igniting temperature and the fuel which now flows from the main burner I0 is ig- 6 nited by the flame from the pilot burner following ignition of the latter by the igniter 40.

As previously mentioned herein the pilot burner 36 could be dispensed with in view of the socalled forced pick-up of the main burner valve 34 when its coil 35 is no longer shunted. It is apparent that this pick-up is not dependent upon the prior heating of the thermal resistor 42 or any othercontingency but is. entirely automatic. Hence, the thermal resistor 42 and the igniter 40 could equally well be located adjacent the main burner I0 instead of the pilot burner 36. The resistance elements 42 and 44 have now become heated, the former due to the flame from the pilot burner and the passage of current therethrough, and the latter due to the passage of current therethrough only. Consequently, the bridge balance is improved to such an'extent that the current through the cut-out 46 is reduced to a value insufiicient to cause operation thereof regardless of whether the main switch is manipulated in on-off-on cycles. At the expiration of the eighteen-second time delay, the switch 56 opens and causes deenergization of the first bridge arm which includes the ignition coil 40 and the adjusting resistor 44. As the solenoid winding 50 is connected in parallel circuit with the latter elements it also becomes deenergized by operation of the time delay switch 56. The bridge nature of the circuit is thus eliminated unless the network is considered a bridge with infinite impedance in one arm. The circuit which now exists for the duration of thenormal running period of the burner consists of the secondary of transformer 84, resistance element 44, and the parallel mesh of thermal resistor 42 and electromagnetic valve coil 35 with the cut-out 46 all connected in series circuit.

Operation of the long time delay switch 56 to open position is entirely automatic and occurs regardless of whether the resistance element 42 is heated by the pilot burner flame or even whether the pilot burner 36 has become ignited. Thus, when the switch 56 opens, unless the ballast resistor 42 has become heated and its resistance increased sufiiciently to raise the resistance of the shunt established thereby around the coil 35 of the electromagnetic fuel valve 34 and cut-out 46 and to compensate for the increase in total circuit resistance, then the current through the electromagnetic valve coil 35wil1 decrease below holding value and the valve 34 will close. If at any time during operation of the apparatus the flame of the pilot burner 36 ceases, then the resistance element 42 will cool and its resistancebe lowered in consequence so that the current through the electromagnetic valve 34 is rendered insufficient to retain this valve in open position. whereupon the closure thereof will occur.

The invention is more particularly directed toward the means for deenergizing the solenoid Winding 50 of the control relay 48 as soon as the circuit timing function is performed. As will be apparent, this is achieved by connecting this winding in parallel circuit With the igniter 40 so that it becomes deenergized by operation of the time delay switch 56 at the same time as the igniter becomes deenergized.

Due to the fact that release of the core 52 by the solenoid winding 50 will serve to return the time delay switches 54, 56 to their initial closed position, it becomes necessary to include the switching means 66, 68 to maintain the winding 50 and the igniter 40 deenergized. These switching means 66, 68 are operatively associated with the core 52 and will be operated to open their contacts l0, l2 and H, 16 whenever the core is released by deenergization of ,the solenoid winding 50. Thus, during the running operation of the burner the power consuming elements, such as the igniter 40 and the solenoid winding 50, are disconnected. The usual source of noise is thus not present during normal running of the burner and the current consumption is correspondingly reduced.

It is further apparent that the simple switching means I8 which is operated to closed position momentarily by the handle l5 will serve to shortcircuit the switching means 68 and cause energization of the solenoid winding 50 during the starting operation when the switching means 88 is open. Thus, the time delay period of the switches 54, 56 can be initiated due to energization of the solenoid winding 50 when the switching means I8 is momentarily closed.

As previously mentioned herein, the type of mercury time-delay switches disclosed are commercially available and no specially designed devices are required to accomplish the purposes of the invention. It may be stated, however, that these switches might be arranged for reverse operation, that is, normally open when the relay is deenergized and closed during the delay periods following energization of the relay. In such event, the switching means 66, 68 could be dispensed with as the circuit would be opened by the mercury switches themselves in this reverse type of operation. However, the switching means It would still be required for short-circuiting purposes during part of the starting period as disclosed herein.

It will be understood that these and various changes can be made in the arrangement and combination of parts and in theform of the elements herein disclosed within the scope of the appended claims without departing from the spirit of the invention.

I claim:

1. A safety control system for fuel burners having a source of electrical energy, comprising electrically operable fuel controlling means movable between fuel flow permitting and preventing positions, means responsive to a condition caused by combustion of the fuel and electrically connected to said fuel controlling means for varying the energy value supplied thereto sufliciently to cause movement thereof to flow preventing position in the absence of combustion, control means adapted to complete an energizing circuit for said fuel controlling means for rendering said condition responsive means ineffective to cause said movement fora predetermined period during which said condition responsive means has time to become responsive, said control means comprising a solenoid and switch means operable thereby for causing deenergization of said solenoid upon expiration of said period, and switching means operable for establishing a circuit including the source and said solenoid for causing energization of said solenoid to initiate said period.

, 2. A safety control system for fuel burners having a source of electrical energy, comprising-electrically operable fuel controlling means movable between fuel flow permitting and preventing positions, means responsive to a condition caused by combustion of the fuel and electrically connected to said fuelcontrolling means for varying the energy value supplied thereto suflici'ently to cause movement thereof to flow preventing position in the absence of combustion, control means adapted to complete an energizing circuit for said fuel controlling means for rendering said condition responsive means ineffective to cause said movement for a predetermined period during which said condition responsive means hastime to become responsive, said control means comprising a solenoid and switch means operable therebyfor assuming an open position and causing deenergization of said solenoid upon expiration of said period, and switching means operable for establishing a circuit including the source and said solenoid for causing enerization of said solenoid to initiate said period irrespective of the open position of said switch means.

3. A safety control system for fuel burners having a source of electrical energy, comprising electrically operable fuel controlling means movable between fuel flow permitting and preventing positions, means responsive to a condition caused by combustion of the fuel and electrically connected to said fuel controlling means for varying the energy value supplied thereto sumciently to cause movement thereof to flow preventing position in the absence of combustion, control means adapted to complete an energizing circuit for said fuel controlling means for rendering said condition responsive means ineffective to cause said movement for a predetermined period during which said condition responsive means has time to become responsive, said control means comprising an electromagnetic device havinga time delay switch adapted for movement from an initial switch position upon energization of said device, said switch movement causing deenergization of said device upon expiration of said period and return movement of said switch to said initial position substantially instantaneously, and means responsive to one of said switch movements for preventing reenergization of said device in said initial position.

4. A safety control system for fuel burners having a source of electrical energy, comprising electrically operable fuel controlling means movable between fuel flow permitting and preventing positions, means responsive to a condition caused by combustion of the fuel and electrically connected to said fuel controlling means for varying the energy value supplied thereto sufliciently to cause movement thereof to flow preventing position in the absence of combustion, control means adapted to complete an energizing circuit for said fuel controlling means for rendering said condition responsive means ineffective to cause said movement for a predetermined period during which said condition responsive means has time to become responsive, said control means comprising an electromagnetic device having a time delay switch adapted for movement from an initial switch position upon energization of said device, said switch movement causing deenergization of said device upon expiration of said period and return movement of said switch to said initial position substantially instantaneously, means responsive to one of said switch movements for preventing reenergization of said device in said initial position, andmeans operable for short-circuiting said last means to cause en ergization of said device in said initial position to initiate said period.

5. A safety control system for fuel bumers having a source of electrical energy, comprising electrically operable fuel controlling means movable between fuel flow permitting and preventing positions, means responsive to a condition caused by combustion of the fuel and electrically connected to said fuel controlling means for varying the energy value supplied thereto sufiiciently to cause movement thereof to flow preventing position in the absence of combustion, control means adapted to complete an energizing circuit for said fuel controlling means for rendering said condition responsive means ineffective to cause said movement for a predetermined period during which said condition responsive means has time to become responsive, said control means comprising an automatic time-delay switch and solenoid operator therefor adapted for movement from initially closed to open position upon energization of said solenoid to render said condition responsive means effective if combustion does not exist, said switch movement causing deenergization of said solenoid upon expiration of said period and return movement of said switch substantially instantaneously to said initial closed position, switching means adapted for movement to open position in response to said return movement of said switch for preventing reenergization of said solenoid in said initial closed position, and second switching means operable for short-circuiting the first said switching means to cause energization of said solenoid in said initial position to initiate said period.

6. An ignition and safety control system for fuel burners having a source of electrical energy, comprising electrically operable fuel controlling means movable between fuel flow permitting and preventing positions, main switch means for controlling energization of said fuel controlling means from the source and operative to cause said movement thereof, means responsive to a condition caused by combustion of the fuel and electrically connected to said fuel controlling means for reducing the energy value supplied thereto sufiiciently to cause movement thereof to fiow preventing positions in the absence of combustion, an electric resistance igniter for the fuel, control means responsive to operation of said main switch to complete an energizing circuit for said fuel controlling means and for rendering said condition responsive means ineffective to cause said movement for a predetermined period during which said condition responsive means has time to become responsive, said control means comprising an electromagnetic device having solenoid and a time delay switch adapted for movement from an initial closed position upon energization of said device to an open position for rendering said igniter inoperative and said condition responsive means effective if combustino does not exist, said solenoid being connected in series circuit with said time delay switch for causing deenergization of said device upon expiration of said period, switching means responsive to a return movement of said time delay switch to initial closed position for preventing reenergization of said device, and second switching means operable by said main switch for shortcircuiting the first said switching means'to cause energization of said device to initiate said period.

7. An ignition and safety control system for fuel burners having a source of electrical energy and main and pilot burners, comprising an electromagnetic valve for controlling the fuel supply to the main burner, main switching means controlling the energization of said valve, a thermal resistor having a preselected temperature coeficient of resistance and being located to be heated by the pilot burner flame, said resistor varying in 10 resistance when heated for causing said valve to close in the absence of said flame, an electric resistance igniter for the pilot burner, a control relay having a solenoid and a pair of timing elements adapted for movement from an initial closed position upon energization of said solenoid to an open position after different delay periods, said periods being sufficient respectively for said igniter to reach igniting temperature and said resistor to become heated, one said element being connected for shunting said valve in closed position and the other said element being connected for causing deenergization of said igniter and solenoid in open position, a pair of initially open switching means operatively associated with said relay for closure thereby upon energization thereof, one said switching means being adapted for maintaining said igniter and solenoid deenergized upon return movement of said timing elements to closed position and the other said switching means being adapted for preventing said shunting of said valve, and a third switching means operative by said main switch for short-circulting said one of said switching means for a period sufficient to cause energization of said solenoid and closing of said pair of switching means by operation of said relay to initiate said delay periods.

8. An ignition and safety control system for fuel burners energizable from a source of current supply and comprising an electric igniter for the fuel connected in a first arm of an electrical bridge circuit, an electrically operable fuel control device in a second arm of said bridge, a pair of resistors in third and fourth arms respectively of said bridge, one of said resistors being exposed to the heat of the burning fuel for varying in resistance and causing variation in the current value supplied to said device, control means including a solenoid and switch means operative for opening and closing said first arm, main switch means operative between off and on positions for connecting the source across opposite junctions of said bridge with said first and second arms and said third and fourth arms in series circuit respectively and in multiple across said junctions, said solenoid being connected in a separate circuit with the source but being adapted to be deenergized by opening of the first said arm, and switching means movable momentarily to closed position during operation of said main switch to on position for establishing another circuit including the source and said solenoid for causing energization of said solenoid.

9. An ignition and safety control system for fuel burners energizable from a source of current supply and comprising an electric igniter for the fuel connected in a first arm of an electrical bridge circuit, an electrically operable fuel control device in a second arm of said bridge, a pair of resistors in the third and fourth arms respectively of said'bridge, one of said resistors being exposed to the heat of the burning fuel for varying in resistance and causing variation in the current value supplied to said device, control means including an automatic time-delay switch for opening and closing said first arm and a solenoid for operating said time-delay switch, said timedelay switch being adapted for movement from initially closed to open position upon energization of said solenoid and return to closed position upon deenergization of said solenoid, main switch means operative between off and on second arms and said third and fourth arms in series circuit respectively and in multiple across said Junctions, said solenoid being connected in parallel circuit with said igniter and adapted to be deenergized therewith by operation of the time-delay switch to open position, switching means in said firstarm and being operatively associated with said control means for movement to open position in response to said deenergization of said solenoid and said return of said time-delay switch to closed position for preventing reenergization of said solenoid, and second switching means movable momentarily to closed position during operation of said main switch to on pol2 sition for establishing another circuit including the source and said solenoid for causing energization of said solenoid to initiate said period.

CHARLES K. STROBEL.

REFERENCES CITED UNITED STATES PATENTS Name Date McCabe Apr. 12, 1932 in the Number 

